Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in the tissue region along the pulmonary veins of the left atrium and in the superior pulmonary veins. In this condition, after unwanted signals are generated in the pulmonary veins or conducted through the pulmonary veins from other sources, they are conducted into the left atrium where they can initiate or continue arrhythmia.
Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. More recently, it has been found that by mapping the electrical properties of the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
In this two-step procedure—mapping followed by ablation—electrical activity at points in the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which ablation is to be performed.
U.S. Pat. No. 6,063,022 to Ben-Haim, which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes an invasive probe including two position sensors in a fixed, known relation to the distal end of the probe. The position sensors generate signals responsive to their respective position coordinates and at least one contact sensor along a radial surface of the probe for generating a signal representing its contact with body tissue to be ablated by electrodes on the probe.
U.S. Pat. No. 6,272,371 to Ben-Haim, which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes an invasive probe including a flexible portion that assumes a predetermined curve form when a force is applied thereto. Two position sensors, fixed to the distal portion of the probe in known positions, are used to determine position and orientation coordinates of at least one of the sensors, and to determine the locations of a plurality of points along the length of the distal portion of the probe.
PCT Patent Publication WO 96/05768 and corresponding U.S. Patent Application Publication 2002/0065455 to Ben-Haim et al., which are assigned to the assignee of the present patent application and which are incorporated herein by reference, describe a system that generates six-dimensional position and orientation information regarding the tip of a catheter. This system uses a plurality of sensor coils adjacent to a locatable site in the catheter, for example near its distal end, and a plurality of radiator coils fixed in an external reference frame. These coils generate signals in response to magnetic fields generated by the radiator coils, which signals allow for the computation of six position and orientation dimensions, so that the position and orientation of the catheter are known without the need for imaging the catheter.
A lasso catheter is disclosed in commonly assigned U.S. Pat. No. 6,973,339, which is herein incorporated by reference. The lasso catheter is particularly adapted for pulmonary vein mapping and ablation. This catheter comprises: a curved section having a first position sensor that is capable of generating fewer than six dimensions of position and orientation information, one or more electrodes, adapted to measure an electrical property of the pulmonary vein; and a base section attached to a proximal end of the curved section. Disposed on the base section within 3 mm of the distal end thereof is a second position sensor, capable of generating six dimensions of position and orientation information.